Crystalline copolymers of ethylene and tetrafluoroethylene having high workability characteristics

ABSTRACT

Crystalline copolymers of ethylene and tetrafluoroethylene of high thermal stability characteristics in the molten state and high resistance to oxidation under heat, having a contact in tetrafluoroethylene from 53 to 63% in moles, homogeneously distributed along the chain axis and among the chains characterized in that the temperature gap between their ultimate melting temperature and the temperature at which oxidative decomposition of the copolymers begins is at least 80*C. They are prepared by polymerization of monomers mixtures having a content in tetrafluoroethylene greater than 78% in moles. The copolymers can be used as plastic materials and are particularly useful since said temperature gap of at least 80*C permits the processing thereof, and the reprocessing of scraps, to useful manufactured articles, conveniently and economically and by conventional techniques.

United States Patent [1 1 Modena et al.

[ CRYSTALLINE COPOLYMERS OF ETHYLENE AND TETRAFLUOROETHYLENE HAVING HIGHWORKABILITY CHARACTERISTICS [75] lnventors: Mario Modena, Bollate; MarioRagazzini, Milan; Giancarlo Borsini, Rome; Marco Valera, Milan, all ofItaly [73] Assignee: Montecatini Edison S.p.A., Milan,

Italy [22] Filed: Aug. 16, 1973 [21] Appl. No.: 388,910

Related U.S. Application Data [63] Continuation of Ser. No. 143,637, May14, 1971, abandoned, which is a continuation-in-part of Ser. No.730,190, May 17, 1968, abandoned [52] U.S. Cl. 260/875 B, 117/161 UZ[51] Int. Cl. C08f 1/06, C08f 15/02 [58 Field of Search 260/87.5 B

[56] References Cited UNITED STATES PATENTS 2,468,664 4/1949 Hanford eta1 260/86 [11] 3,870,689 [451 Mar. 11, 1975 3,528,954 9/1970 Carlson260/883 R 3,738,923 6/1973 Carlson et al. 260/875 B Primary Examiner-H.S. Cockeram [57] ABSTRACT Crystalline copolymers of ethylene andtetrafluoroethylene of high thermal stability characteristics in themolten state and high resistance to oxidation under heat, having acontact in tetrafluoroethylene from 53 to 63% in moles, homogeneouslydistributed along the chain axis and among the chains characterized inthat the temperature gap between their ultimate melting temperature andthe temperature at which oxidative decomposition of the copolymersbegins is at least 80C. They are prepared by polymerization of monomersmixtures having a content in tetrafluoroethylene greater than 78% inmoles.

The copolymers can be used as plastic materials and are particularlyuseful since said temperature gap of at least 80C permits the processingthereof, and the reprocessing of scraps, to useful manufacturedarticles, conveniently and economically and by conventional techniques.

2 Claims, N0 Drawings CRYSTALLINE COPOLYMERS OF ETHYLI INE ANDTETRAFLUOROETHYLENE HAVING HIGH WORKABILITY CHARACTERISTICS This is acontinuation-in-part of our application Ser. No. 730,190, filed on May17, 1968 (now abandoned), and a continuation of our application Ser. No.143,637 filed May 14, 1971 (now abandoned), in which we disclosedcrystal-line polymeric materials with high workability characteristics,constituted by copolymers of ethylene and tetrafluoroethylene with acontent in tetrafluoroethylene varying from 53 to 63% by moles.

THE PRIOR ART It is known that polytetrafluoroethylene, although havinggood characteristics such as a high melting temperature, a highstability to all chemical agents, even at a high temperature, as well asa very low friction difficult is difficular to process by conventionaltransforming techniques (extrusion, injection moulding and the like) andspecial techniques are required.

The copolymers of tetrafluoroethylene and ethylene of the known types donot have altogether satisfactory thermal stability characteristics inthe molten state and show a poor resistance to ageing in the air and athigh temperatures below their melting point. As a matter of fact, suchcopolymers, after having been exposed to the action of air at hightemperatures (l50200C) already after a few days show a degrading oftheir mechanical characteristics (tensile strength, elongation at break,etc.) of such a degree as to discourage their use in those applicationswhich require a good preservation of the mechanical characteristics alsoafter their use at a high temperature for long periods of time.

It is also commonly accepted that tetrafluoroethylene-ethylenecopolymers having high tetrafluoroethylene content possess high meltingpoints and are untractable or very difficult to be processed in that thedifference between the flow temperature and the thermal-deteriorationstarting temperature is small (U.S. Pat. No. 3,445,434 page 1, column 2,lines 67-72 and Brit. Pat. No. 1,024,351, page 1, lines 3565).

Thus, an object of this invention is that of providing crystallinepolymeric materials containing fluorine which are free of the drawbackspreviously described.

Other objects will appear hereinafter.

These objects are accomplished'by means of copolymers of ethylene andtetrafluoroethylene which, according to this invention, arecharacterized by a content in tetrafluoroethylene, homogeneouslydistributed along the polymeric chain and among the chains, varying from53 to 63% moles.

The materials according to this invention are crystalline products witha melting point surprisingly decreasing, and a decomposition temperatureconversely, increasing, as the final content in tetrafluoroethyleneincreases. Thus, the most outstanding and distinguishing characteristicof the present thermally stable and oxidation-resistant crystallinecopolymers of ethylene and tetrafluoroethylene containing an amount oftetrafluoroethylene in the specific range from 53 to 63% by moleshomogeneously distributed along the polymeric chain axis and among thechains is the temperature gap between the ultimate melting temperatureof the copolymers and the temperature at which oxidative decompositionof the copolymers begins. The temperature gap is C or more. (Themeasurement method is described in example 6).

The gap between the ultimate melting temperature and the temperature atwhich oxidative decomposition sets in is of great practical importancein the commercial use of tetrafluoroethylene/ethylene copolymers. It isat the temperatures in the range between ultimate melting of thecopolymers and the onset of oxidative decomposition that the copolymerscan be processed to useful manufactured articles by conventional shapingtechniques, including extrusion and injection molding. The temperaturegap must be sufficient to permit obtaining the manufactured shapedarticles and the reprocessing of scraps. It is actually the widetemperature gap as hereinbefore defined that allows the materialsaccording to this invention to exhibit a particularly high thermalstability at the processing conditions. As a matter of fact, theirmelt-flow index sufers only small variations, even after repeatedextrusion at temperatures considerably higher than the melting point ofthe copolymer.

The whole of these characteristics makes it surprisingly possible toeasily work these polymeric materials with the normal conventionaltechniques and on the usual equipment normally used for the commonthermoplastic materials such as polyethylene, polyvinyl chloride and thelikes.

These materials are furthermore characterized by a particularly highresistance to oxidation. In fact, samples of these materials subjectedto oxidation tests by air at l50-200C show a very low degrading of themechanical characteristics, so much so as to allow the use of thesemoulded objects also for those applications for which resistance to hightemperatures and resistance to oxidation are required.

On the contrary, the polymeric materials according to the prior art,with an average content in tetrafluoroethylene different from thatforeseen by the present invention, do not possess such properties as tobe easily workable, nor such a good thermal stability as to be employedunder heavy temperature conditions.

It has been found in fact, as it will be apparent from the examples,that the melting temperature of the tetrafluoroethylene/ethylenecopolymers increases with increase of the tetrafluoroethylene content atvalues below 50 moles percent, and decreases with increase in thetetrafluoroethylene content at values above 50 moles percent, and thatthe oxidative decomposition temperature is substantially independent ofthe composition of the copolymers when the tetrafluoroethylene contentis less than 46 moles percent, and vice versa, increases when thetetrafluoroethylene content is higher than 46 moles percent. Moreparticularly, it has been found that the content of from 53 to 63% bymols of tetrafluoroethylene in the present products, is critical toobtaining the copolymers showing a difference of 80C or more between theultimate melting temperature and the temperature at which the oxidationdecomposition starts.

The copolymers according to this invention may be used for thoseapplications, such as pipe lines for corrosive liquids and organicsolvents, gaskets, mechanical parts, electrical insulations andcoatings, which must be used at high temperatures and/or in the presenceof chemical reactants and solvents.

A particularly advantageous use of the copolymers according to thisinvention is represented by the transformation into films and fibers ofhigh characteristics.

The copolymers according to this invention are obtained by thecopolymerization of starting monomeric 88mg mixtures having contents intetrafluoroethyl ene greater Tensile strength in kg/cm: 485 295 than 78%moles and the composition of which is mam- 5 Elongation at break 307 61tained constant during the copolymerization reaction by means ofappropriate monomer additions.

It has been found, in fact, as will be apparent from The ebove reporteddata h that the copolymers the examples hereinbelow, that when astarting monoeeeerdlhg to the know" teehmquer after 30 y f meric mixturehaving a lower tetrafluoroethylene con mg m an f Presented? Y markeddegrading of tent is subjected to copolymerization, copolymers are themechanical characteristicsobtamed wherein the mol percent content ofcopoly- EXAMPLE 2 merized units of tetrafluoroethylene IS outside thelower limit of the defined and critical, molar percent Into the Samereactor as that described Example 1 range of the present copolymers. 5were continuously fed in a mixture of monomers con- Othercharacteristics of the copolymers of this inventaining 79 0f rfluoroethylene and 2 l% of ethylene tion will also be evident from thefollowing examples and a iX l e O 480 Of Wa and 0 CC/ O which are givento illustrate the invention and are not tertiary butyl alcohol. intendedto be limiting. The mixture water/tert. butyl alcohol contains dissolved100 m /l of a mixture of ammonium ersul- EXAMPLE 1 h g p p ate.

An ethylene/tetrafluoroethylene copolymer of a The reaction temperaturewas maintained at 65C, known type containing 44% moles oftetrafluorwhile the pressure amounted to 40 kg/cm oethylene wasprepared. A stainless steel autoclave of The average reaction time was 1hour.

6 litres capacity, equipped with a stirrer and a thermo- From thereactor was continuously drawn the polystabilizing sleeve was emptied ofoxygen by means of mer, which was washed, filtered and dried. repeatedwashings with nitrogen. In this autoclave were In this way were obtained440 g/h of polymer which introduced in this Ordefi showed thecharacteristics reported on the following Table II:

150 g distilled water TABLE I1 3000 g tetriary butyl alcohol 500 gtetrafluoroethylene 130 g ethylene Contents in tetrafluoroethylene 53it; moles 0.5 g ammonium persulphate dissolved in 150 g of water.Optical mehmg P 277 C Tensile strength 465 kg/cm Elongation at break 322The starting monomeric mixture contains, thus, 55% Melt-flow index at330C 6.0 g/IO min. moles of tetrafluoroethylene and 45% moles of ethyl-Inhaled P See 2 ene. The reaction mixture was then heated up to 65Cwhile the pressure attained 28 kg/cm After 2 hours the autoclave wascooled down and E i i of thls gP g eg f as flesFnbed then opened. Thepolymer was washed with boiling wa- 40 xamp e were 5 lecte to agemg m anter filtered and dried flow oven at 190 C for 30 days.

In this way were obtained 139 g of a copolymer hav- After l agemg hsamples of FoPolymer Showed ing the characteristics recorded on thefollowing Table the followmg mechamcal charactenstlcs:

I TABLE 1 Initial After ageing Tensile strength in kg/cm 465 435Contents in tetrat'luoroethylene (l) 44 moles Elongation at break in 32334 Optical melting point (2) 269C Tensile strength (3) 485 kg/cmElongation at break (3) 307 Me:t-gow ngex at 338:2; (Z; 8-2 gm; m- Othersamples were subjected to artificial ageing in f ggi' 13 3 3;, E 5 %09fi 'g' z an airflow oven at 190C for 60 days. After this ageingTemperature at which the torsional modulus is the samples showed thefollowing characteristics: equal to l.l0 dine/cm (5) 228C Infraredspectrum (6) see FIG. I

(l) Elementary carbon analysis lnlllfll After ageing (2) Disappearanceof double refraction ASTM D21 I7-62- (3) ASTM D l708-S9 T stretch rate 5cm/min Tensile strength in kg/cm 465 444 (4) ASTM D 1238-65 T appliedload 6 kg lcm Elongation at break in 322 378 (5) Dynamic-mechanicalmeasurements; freguence=l cycle/sec. (6) Measurements carried out on afilm (with Perkin-Elmer Mod. 21 spectrophotometer having a prism ofNaCl).

From this artificial ageing test it appears quite clearly Samples ofthis copolymer were prepared accordin that the copolymers according tothe invention suffer to the procedures described by the ASTM D 1708-59only very slight variations of the mechanical properties T rules, whichsamples were then submitted to artificial even after long resting timesin the air-flow oven at ageing through heating in an airflow oven at190C for lC. This means that the materials according to this 30 days.

The samples thus treated showed the following mechanicalcharacteristics:

invention show a very good resistance to the combined action of air andheat, far much superior to that of the copolymers obtained according tothe prior art.

EXAMPLE 3 Into the reactor described in Example 1 were continuously fedin a mixture of monomers containing 81% of tetrafluoroethylene and 19%of ethylene and a mixture of 400 cc/h of water and 3600 cc/h of tertiarybutyl alcohol. This water/tertiary butyl alcohol mixture containeddissolved in it 67 mg of ammonium persulphate for each litre of mixture.

The reaction temperature was maintained at 62C while the pressureamounted to 42 kg/cm The average or mean reaction time was 1 hour.

From the reactor is continuously drawn the polymer which is then washed,filtered and dried.

In this way were obtained l54 g/h of polymer which showed thecharacteristics reported on the following Table III.

Samples of this copolymer, prepared as described in Example I, weresubjected to artificial ageing in an airflow oven at 190C for 30 days.

After this ageing the samples showed the following mechanicalcharacteristics:

Initial After ageing Tensile strength in kg/cm 478 412 Elongation atbreak in 303 3l3 Other samples were subjected to an artifical ageingtest in an airflow oven at l90C for 60 days. After ageing the samplesshowed the following mechanical characteristics:

Initial After ageing Tensile strength in kg/cm 478 396 Elongation atbreak in 303 3l8 Initial After treatment Tensile strength in kg/cm 478466 Elongation at break in 303 278 A copolymer similar to the precedingone and having a contents in tetrafluoroethylene of 55% in moles,

showing a melt-flow index of 4.4 g/lO min. at 330C and of 2.2 at 300C,was extruded 10 times at 330C on the melt-flow index apparatus describedin Example 1; after this treatment the copolymer showed a melt-flowindex of 5.4 g/lO minutes at 330C.

The same copolymer was granulated in a Bandera extruder of the type 30mm o L/D 17 at a temperature of 325C and showed the followingcharacteristics:

Tensile strength in kg/cm Elongation at break in Melt-flow index at 300Cg/l0 min.

Moore After l0 extrusions in the Brabender Plastograph at 330C thecopolymer showed the following characteristics:

Tensile strength in kg/cm 480 Elongation at break in 275 Melt flow indexat 300C g/l0 min. 2.8

All these tests showed that the copolymers according to this inventionpresented an excellent'resistance to ageing and an excellent thermalstability.

EXAMPLE 4 In a stainless steel autoclave of 6000 cc capacity, providedwith a stirrer and a thermostabilizing sleeve, and freed of the oxygenby repeated washings with nitrogen, a mixture was subjected topolymerization which was constituted by:

of distilled water 2900 g of tertiary butyl alcohol I320 g oftetrafluoroethylenc 76 g of ethylene 0.2 g of ammonium persulphate.

TABLE IV Contents in tetrafluoroethylene 58% in moles Optical meltingpoint 270C Tensile strength 442 kg/cm Elongation at break 317% Melt-flowindex at 300C Torsional modulus at 23C Temperature at which thetorsional modulus is equal to L10 dine/cm Infrared spectrum 7.5 g/l0minutes 3.7 10 dine cm 235C see FIG. 4

Samples ofthe polymer thus prepared were subjected to successiveextrusions in a Brabender Plastograph extruder; after 10 extrusions at330C the polymer showed the following characteristics:

After Initial extrusion Tensile strength in kg/cm 442 440 Elongation atbreak in 317 260 Melt-flow index at 300C g/IO min. 7.5 7.5

As can be seen from the above data the copolymer maintains practicallyunaltered the tensile strength and the melt-flow index, while it shows amodest variation of elongation at break. This stands to prove the highr'e- It is assumed that the stress conditions which the copolymerundergoes during the above reported test which consisted in extrusionson the melt-flow index apparatus at a temperature of 80C greater thanthe opsistance characteristics of the copolymer under the 5 i l l ipoint of h copolymer, may b id- C n s at which It n be transformed intomanuered comparable to the stress conditions which the coactu e 5.polymer undergoes during the processing of the co- EXAMPLE 5 polymer(extrusion, moulding etc.)

10 As known, the melt-flow index is generally consid- Into the reactorfieserlbed Example 1 e e eohtlh' ered as an index inversely proportionalto the molecuuously fed a mixture of monomers eohtalhlhg 90% lar weightof the polymer. Thus, an increase of the moles of tetrafluoroethyleheand 10% moles of y melt-flow index is interpreted as a decrease of themoene, and a mixture of 360 cc/h water and 26 40 CC/h lecular weightattributable to a degradation phenome- Of tertiary alcohol contamlng disSolved In It non aused the prolonged heating at a temperamg of ammomum pp for h f of mlxtul'eture which, in this particular case, is about 80Chigher The temperature of reaction was mamtamed at 65C than the i lmelting point f the copolymer and h Pressure was p at 60 kg/emz- Theaverage From the above reported table it can be seen how the Teachertlme was 1 hour copolymers of this invention show a very low increaseFrom the reactor p y cohtlhuously of the melt-flow index, that is, notgreater than 30%. draWh Washed, filtered and q Thereby were Thecopolymers according to the prior art represented 'he 280 g/h of e p yWh Showed the Charby the copolymer at 44% in moles oftetrafluoraeterlshes recorded the followmg Table VI oethylene describedin Example 1, show a considerable increase of the melt-flow index. Itcan thus be re- TABLE V marked that the copolymers according to thisinvention Contents in mmfluomethylene 60 in moles show a stabilityduring the forming or moulding pro- Optical melting point 264C cessesfar greater than that of the copolymers of the Tensile strength 382kg/cm rior an Elongation at break 339 P Melt-flow index at 270C 4.! g/lOmin. In order to evaluate by an alternative method to the Melt-flowindex at 330C 15.6 g/10 min. Infrared Spectrum See FIG. 5 preceding oneof the stab1l1ty characteristics during forming, the copolymers preparedas described herein above, were subjected to 10 successive extrusions inSamples of this polymer prepared as described in Exthe above p fimelt'flow index apparatus at l ample l were subjected to artificialageing in an airflow Perature of 330 The followlhg results wereobtalhedi oven at 190C for 30 days. After this ageing the sample showedthe following mechanical characteristics:

Contents in Melt-flow Melt-flow index variation moles of tetraindex atat the tenth of the lhmal After agelhg fluoro ethylene the firstextrusion melt-flow extrusion index Tensile strength in kg/cm 382 317 40Elongation at break 339 391 44 0,9 1,5 +6671 53 6.0 8.4 +40 55 4.4 5.4+227 56 9.0 11.0 +223 From the above reported data it W1" be seen thatthe 60 I815 HM copolymer shows a good resistance to the combined actionof air and heat.

In order to evaluate the stability of the copolymers, the copolymersprepared according to the preceding Also this method brings intoevidence the superiority examples were subjected to 5 successiveextrusions in of the thermal stability of the copolymers according to anapparatus for determination of the melt-flow index the invention incomparison to the copolymers preaccording to the rules of ASTM D 1238 65T. (appared according to the prior art. plied load), 6 kg/cm at atemperature of about 80C The infrared spectra of comparison mouldedfilms of above the optical melting point of the polymer and the thecopolymers described in examples 1-5 have been following data ofmelt-flow index were obtained, exregistered with a Perkin-Elmer Mod 21double beam pressed as grams of polymer extruded in 10 minutes.spectrophotometer (prism 2 NaCl; resolution 9,27;

Example 70 contents in optical extrusion Melt-flow Melt-flow variationmoles of melting temperatindex on index on of tetrafluoropoint ure inthe 1st the 5th melt-flow ethylene C C extrusion extrusion index gain5.8; pen traverse time: 3 seconds; response 1) and are shown in thescans obtained.

The infrared spectrum bands whichshow the sequences of the ---Cl-lgroups are located in corre spondence with the frequencies:

773 cm whose intensity is proportional to the number of (--Cll groups733 cm whose intensity is proportional to the number of (Cl-l groups 721cm whose intensity is proportional to the number of (---CH groups with n4.

For each copolymer it is thus possible to calculate the ratio betweenthe absorbances of the bands:

copolymer was found to contain 38.6% of carbon corresponding to atetrafluoroethylene to ethylene mol ratio of 47.5 52.5 percent.

(b) A group of tetrafluoroethylene-ethylene copolymers containing from36 to 63 moles per cent of tetrafluoroethylene were synthetized underthe conditions disclosed in Table VI.

The infrared spectra of compression molded films of the samples obtainedas described in (a) and (b) above have been registered as abovedescribed (page 18). Film thickness has been selected to give anabsorbance value of the band at 773 cm comprised between 0.04 and 0.15.

Molar 7 of tetrafluoroethylene in the copo (loglO/l) 733 (log lo/l) 773(log lo/l) 721 (log lo/l) 773 From the above listed data it can be seenthat in the copolymers according to this invention, that is, having acontent in tetrafluoroethylene comprised between 53% and 63% thesequences (CH with n 4 and those with (---CH;.),, are present in veryreduced quantities and are by far inferior to those present in thecopolymers according to the prior art. Furthermore, in the copolymersaccording to the invention, the sequences (-CH are present in a greaternumber.

This actually means that the copolymers according to the invention havea more homogeneous structure and that the ethylene molecules are moreregularly distributed along the axis of the polymeric chain.

EXAMPLE 6 This example illustrates in section (a) the preparation of anethylene/tetrafluoroethylene copolymer according to prior art, insection (b) the preparation of a group of copolymers having anincreasing content of C 1, by mols, and then presents a comparison ofthe characteristics of the copolymers prepared in (a) and (b):

(a) A stainless steel high pressure reactor having a capacity of about2800 parts by volume was flushed with tetrafluoroethylene and then 175parts of deoxygenated water, 1225 parts of tertiary butyl alcohol, and1.05 parts of ammonium persulphate were charged into said reactor.Thereafter the reactor was closed and evacuated, then charged with amixture of tetrafluoroethylene and ethylene having a mo] ratio of 120.82as determined by gas chromatographic analysis. The contents of thereactor were stirred and heated at 50C while maintaining an internalpressure of kg/cm (about 350 lbs/sq.in.) by the periodic injection ofthe tetrafluoroethylene/ethylene mixture; the heating and stirring werecontinued for 1.5 hours, and then the reactor was cooled, the pressurereleased and the product discharged, obtaining anethylene/tetrafluoroethylene copolymer in the form of a thick slurrywhich was coagulated by steam distillation, washed and dried. 120 partsof ethylene/tetrafluoroethylene copolymer were obtained and the Theratios between the absorbances of the band at 773 cm are reported inTable Vll. Said ratios are affected by a 30% error.

Samples of the copolymers obtained as described in (a) and (b) above, inpowder form, were analyzed twice with a Du Pont 900 Thermal Analyzer,using a Du Pont D S C cell (Catalog No. 900600) and standard aluminumsample holders, in which analysis the reference was an empty standardsample holder, the heating rate was 15C/minute, the abscissa scale was50C/inch and the ordinate scale was 0.2C/inch. The runs were carried outin static air atmosphere, and the starting temperature was roomtemperature. The samples, as described above are shown wherein:

the thermogram of the copolymer of Run(b) l of Table I containing 36 bymoles of QR;

the thermogram of the copolymer of Run (b) 2 of Table 1 containing 46%of moles of C F the thermogram of the copolymer of Run (b) 3 of Table Icontaining 48 by moles of C 1 the thermogram of the copolymer of Run (b)4 of Table l containing 51 by moles of C F the thermogram of thecopolymer of Run (b) of Table l containing 55 by moles of C F thethermogram of the copolymer of Run (b) 6 of Table I containing 63% bymoles of C F the thermogram of the copolymer of the Run of Example 6 (a)of Table 2 containing 47.5% by moles of C F The temperature valuesreported on the abscissa shown in said thermograms are uncorrectedvalues: the temperature values of the single points reported in thediagram obtained have been corrected using the Chromel-Alumen tablessupplied with the instrument. The thermograms show an en dothermic peakascribed to the melting process and an exothermic slope ascribed to anoxidative decomposition process.

The reproducibility of the melting temperature was within 1C, for theoxidative decomposition onset temperature was about 3C.

The data demonstrated by said thermograms are shown in Table VIII Thedata tabulated in the third and fourth columns of Table Vll combinedwith the data referring to the tetrafluoroethylene content by moles tentof the copolymer above 46% by r'noles and is optipercent in the polymerthat are shown in the last colmum, greater than 80C, for the copolymersaccording umn of Table VI show that the maximum melting temto thisinvention and containing from 53 to 63% by perature and the end ofmelting temperature of the moles of tetrafluoroethylene as it can beseen from the tetrafluoroethylene/ethylene copolymers increase with dataof the last colume of Table VIII. increase in the tetrafluoroethylenecontent at values on the other hand copolymers containing 46% by below50 moles percent and decrease with increase 1n mols or less oftetrafluoroethylene dlsplay the behavgrg f g fl gi gggfgz gg gzfi z isrs ig iour that in the prior art was believed to be common to p alltetrafluoroethylene-ethylene copolymers. In said codative decompositiononset temperature appearing in polymers containing 46% by mols or lessoftetrafluop fifth column of Table vm that the decompw oethylene, thegap decreases with increase in the tetra- Smon im substamlauyIndependent of the fluoroethylene content. This is more apparent fromthe compfsmon of l copolymers when the tetrafluqr' curve obtained whenthe difference between the end of oethy ene Content Is less.than 46moles percent. i mthe melting temperature range and the temperature atcreases when the tetrafluoroethylene content higher 15 which theoxidative decomposition of the copolymers than 46 .moles i begins isplotted against the mole percent of the tetra- The differences inmelting temperature and decomfluometh lene in the co 0] met positiontemperature characteristics due to the tetrafluy p y oroethylene contentin moles percent in the copoly- From the above data in the thermographs,in Table mers shown that the gap between the values of the ulti- V andand the curves referred It IS pp mate melting temperature and thetemperature at that the tetrafluoroethylene/ethylene copolymers of whichoxidative decomposition ofthe copolymer sets in t inventlofl e en i elyere f he known increases with increase in the tetrafluoroethyleneconethylene/ raflu roethyl ne C P IY I' TABLE VI Initial final PolymerRun monomer monomer feed pressure K 8 0 CCI F C ClF time latex carbon CF composition composition kg/cm grams ml ml hrs. polymer content moles71 C F moles 7o C F. moles content weight weight l 15 36 10.5 240 0 4l4- 44.6 36 2 35 40 7 130 3 20 39.4 46 3 84 5O 22 7 30 170 3.5 17 30.348 4 66 5l 2] 7 240 O 3 I8 37.1 5] 5 55 20 L75 I00 3 23.5 35.5 55 6 9462 14 1.75 50 I50 3.75 2l 32.5 63

autoclave capacity 6.7 litres water 3.3 lilrcs sodiumperlluoro-octunonte 7 g reaction temperature 75C TABLE VII Sam le Run(log Io/l) 733/(log lo/I) 773 (log Io/I) 72l/(log Io/I) 773 num er fromTable VI Example 6(b) l 5.0 4.5 2 1.2 0.8 3 0.35 0.l5 4 0.27 0.l5 5 0.150.l5 6 0.l5 0.l5 Copolymer of Example 6(a) 0.55 0.15

(*) Powder in KBr TABLE VIII Difference between Sample Run Melting peakOxidative end of melting number Melting onset maximum End of meltingdecomposition and oxidative from Table VI temperature temperaturetemperature onset temperadecomposition 0n- Example 6(b) C C C ture C settemperature 1 1025; I21 l84.5 204.5 292.5 88 2 224.5 256 261.5 292.5 3l3 239 279 285 348 63 4 244 278 282.5 352 69.5 5 243 265 272 378 106 6236 256 261 424 I63 Copolymer of Example 6(a) 246 277 280 3 l6 5 36 Itwill be apparent that some changes in details may be made in practicingthe invention. Therefore, we intend to include in the scope of theappended claims all variations which will be obvious to those skilled inthe art from the description and working examples given herein.

What we claim is: t

l. A process for preparing crystalline ethylene/tetrafluoroethylenecopolymers containing from 53 to 63% by moles of tetrafluoroethylenehomogeneously distributed along the copolymeric chain axis and among thechains, having a high degree of thermal stability, and showing atemperature gap of at least 80C, measured by differential thermalanalysis, between their ultimate melting temperature and the temperatureat which oxidative decomposition of the copolymers begins, said processbeing characterized in that the starting mixture of ethylene andtetrafluoroethylene which is copolymerized to obtain the copolymerscontains more than 78% of tetrafluoroethylene by moles and theconcentration of tetrafluoroethylene in the mixture of monomers ismaintained above 78% by moles and essentially during thecopolymerization reaction.

2. Crystalline copolymers of ethylene and tetrat'luoroethylenecontaining from 53 to 63% by mols of tetrafluoroethylene in which theunits derived from the tetrafluoroethylene are distributed essentiallyhomogeneously along the copolymeric chain axis and among the copolymericchains, said copolymers having a high degree of thermal stability andresistance to oxidation under heating, and being further characterizedin that the temperature gap between the ultimate melting temperaturethereof and the temperature at which oxidative decomposition of thecopolymers begins is at least 80C, measured by differential thermalanalysis.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5, 7 69 Dated March 11, 1975 Inventor(s) Mario Modena et al It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Col. 1, the heading is amended to recite:

Col. 1, line 18, the word -coefficientis inserted after -riction line19, "difficular" is corrected to -diicult- Col. 2, line 8, "copolymers"is corrected to -copolymer- Col. 4, next to last line, between' f -n and"superior", the Word "much" is cancelled.

Col. 5 line 59, the words -the rnaterialare inserted before "showed,"(1st word).

Col. 11, line 20, before the word "that" the word "shown" is correctedto -show- Col. 12,1ine 5, the word "colurne" is corrected to -column-Col. 14, line 4, the word "constant" is inserted after "essentially".

Signed and sealed this 27th day of May 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officerand Trademarks ORM PO-OSO (10-69) uscoMM-DC 60376-P69 u s. eovznrmsmrsmmm; omcz; 93 0 -Claims priority of Italian application No. 16, Z20,filed May 18, 1967-

1. A PROCESS FOR PREPARING CRYSTALLINE ETHYLENE/TETRAFLUOROETHYLENE COPOLYMERS CONTAINING FROM 53 TO 63% BY MOLES OF TETRAFLUOROETHYLENE HOMOGENEOUSLY DISTRIBUTED ALONG THE COPOLYMERIC CHAIN AXIS AND AMONG THE CHAINS, HAVING A HIGH DEGREE OF THERMAL STABILITY, AND SHOWING A TEMPERATURE GAP OF AT LEAST 80*C, MEASURED BY DIFFERENTIAL THERMAL ANALYSIS, BETWEEN THEIR ULTIMATE MELTING TEMPERATURE AND THE TEMPERATURE AT WHICH OXIDATIVE DECOMPOSITION OF THE COPOLYMERS BEINGS, SAID PROCESS BEING CHARACTERIZED IN THAT THE STARTING MIXTURE OF ETHYLENE AND TETRAFLUOROETHYLENE WHICH IS COPOLYMERIZED TO OBTAIN THE COPOLYMERS CONTAINS MORE THAN 78% OF TETRAFLUOROETHYLENE BY MOLES AND THE CONCENTRATION OF TETRAFLUOROETHYLENE IN THE MIXTURE OF MONOMERS IS MAINTAINED ABOVE 78% BY MOLES AND ESSENTIALLY DURING THE COPOLYMERIZATION REACTION.
 1. A process for preparing crystalline ethylene/tetrafluoroethylene copolymers containing from 53 to 63% by moles of tetrafluoroethylene homogeneously distributed along the copolymeric chain axis and among the chains, having a high degree of thermal stability, and showing a temperature gap of at least 80*C, measured by differential thermal analysis, between their ultimate melting temperature and the temperature at which oxidative decomposition of the copolymers begins, said process being characterized in that the starting mixture of ethylene and tetrafluoroethylene which is copolymerized to obtain the copolymers contains more than 78% of tetrafluoroethylene by moles and the concentration of tetrafluoroethylene in the mixture of monomers is maintained above 78% by moles and essentially during the copolymerization reaction. 